Long-term effects of psychotherapy in children and adolescents: Protocol of a database development and systematic review in the LaKiJu META project

Introduction. Approximately one in every six children and adolescents is affected by mental disorders, which impose significant costs on patients, their families, and societies. Psychotherapy is the first-line treatment for many of these disorders, and systematic reviews of post-intervention effects show small to moderate favorable outcomes compared to control groups. However, the long-term effects of psychotherapy remain less well understood.Methods and analysis. The LaKiJu META project aims to address this gap by developing an open-access database, which will subsequently be used for data synthesis. This database will be established through literature searches in nine databases for (cluster) randomized controlled trials (RCTs) investigating the long-term effects (≥6 months) of any type of psychotherapy in school-aged children and adolescents (ages 6;00 to 17;11 years) with mental disorders. Outcomes will be prioritized based on their relevance to patients, caregivers, and clinicians, and will encompass a broad range of measures, including symptom changes, response rates, and reliable changes. Syntheses will use multilevel meta-analyses to compare intervention and control groups at follow-up assessments, across both transdiagnostic and disorder-specific symptom outcomes. In secondary analyses, we will examine changes within intervention groups over time. Moderator analyses will focus on the effects of study-, intervention-, and patient-level characteristics.Ethics and dissemination. Ethical approval will be obtained for public involvement. For dissemination, we will employ tailored strategies to reach researchers, clinicians, patients and their caregivers, with all groups involved in the development of dissemination plans.Registration details. Preregistered on March 10, 2025, via PROSPERO (ID: CRD420251003208).